Our first major objective is to conduct a detalied ultrastructural study of the peripheral auditory nerve system. the main emphasis to date has been placed on a description of the human (postmortem) spiral ganglia, using serial sections to determine the various types. In both human and squirrel monkey ears the nerve density is being determined at the habenula area and also in Corti's tunnwl. Thus, the relative nerve populations oor both the inner and outer hair celd groups will be established throughout the cochlear length. Our second major objective is to advance our current knowledge on endolymphatic hydrops and Meniere's disease. We have performed sacculotomy on the inner ears of animals with induced endolymphatic hydrops in an attempt to decompress the existing hydrops. Reopening of the blocked endolymphatic duct was also performed for the same purpose. We have conducted a detailed ultrastructural study of the organ of Corti removed (postmortem) from a Meniere's patient for the determination of the cause of deafness. We intend to do scanning electron microscopy of endolymphatic hydrops and normal specimens in various species, including the human.